1. Field of the Invention
The present invention relates to a laser processing apparatus improved in reliability and suited for mass production. The present invention also relates to a reliable laser annealing process suited for mass production, which yet yields low fluctuation and high production yield. In particular, the present invention relates to an annealing process for silicon films, and to a step for crystallizing an amorphous film or a film in a nearly amorphous state, as well as to a step for activating silicon films which were considerably damaged in crystallinity due to ion irradiation, ion implantation, ion doping, etc.
2. Prior Art
Recently, studies on lowering the process temperature for fabricating semiconductor devices and on increasing the area of the devices are extensively performed. In particular, much attention is being paid to laser processing techniques such as laser scribing (cutting thin film samples and the like by irradiating a high energy laser beam to the thin film), laser annealing (irradiating a high energy laser beam to the surface of the sample to effect surface crystallization and the like on the sample), and laser doping (diffusing impurities and the like by irradiating a high energy laser beam to the surface of the sample), as ultimate low temperature processes for treating large area devices.
Researchers of laboratory scale have been conducted to present, however, many problems concerning the application of laser processing technology to mass production have been left out of consideration. For instance, no technology for reducing malfunction and minute displacement of the sample during the laser beam irradiation nor technology for easily irradiating the laser beam to the desired portion has been developed to present.
In particular, large area processes can be effected more efficiently by irradiating laser beams in stripes while moving the sample along one direction. Since the sample movement is confined in a single direction, the movement of the sample can be more easily and simply controlled as compared with a process in which a spot laser beam is scanned over the sample. To make the process more suited for mass production, however, the sample must be moved on a stage driven by a step motor or a servomotor. This inevitably vibrates the sample, and the stage vibration is transferred to the laser apparatus. Accordingly, the vibration of the laser apparatus causes the laser output to fluctuate. However, no drastic solution for such a problem has been proposed to present. Moreover, no profound consideration has been given to the method of sample alignment in using stripe-emitting laserst,
Furthermore, no sufficient study on the conditions for laser annealing has been made so far. Thorough study on such conditions has been neglected under the excuse of greatly varying conditions which depend on the individual apparatuses and the deposited films. Accordingly, it has been generally believed that a laser annealing technology is of no practical use due to the lack of reproducibility and stability.
An object if the present invention is to provide a laser annealing process furnished with novel conditions, so that it may yield reproducible results.
Another object of the present invention is to provide a laser processing apparatus having a particular structure which prevents the vibration of the stage from being transferred to the laser apparatus.
A still another object of the present invention is to provide an optimal method for sample alignment.
The present inventors have studied optimal conditions for laser annealing thin films having initially such a low crystallinity as to make its application as a semiconductor impossible, or thin films of reduced crystallinity due to processes such as ion irradiation, ion implantation, and ion doping, to thereby crystallize and activate them and to impart them properties so that they may function sufficiently as semiconductors. As a result, it has been found that the optimal conditions vary not only by the energy of the laser radiation but also by the pulse width and the wavelength thereof.
The present invention comprises activating a thin film 2 xcexcm or less in thickness and containing silicon as the main constituent by laser annealing, and the process comprises, by taking the light transmittance of the film into consideration. irradiating a short wavelength laser beam 400 nm or less in wavelength.